Crohn's disease, the cause of which is not known, is called inflammatory bowel disease which includes ulcerative colitis as well. When abdominal pain, diarrhea, weight loss, fever and the like are seen continually in young individuals (in their late 10s to early 20s), this disease should be suspected. Diagnosis is based on a combination of clinical symptoms, radiography, and endoscopy or pathological examination, etc. However, these techniques require experience and expertise, and hence diagnosis may be difficult in some cases. In particular, in an early stage of the disease, it is difficult to distinguish Crohn's disease from ulcerative colitis in many cases. On the other hand, gastrointestinal radiography and endoscopy, which are the principal diagnostic techniques, are disadvantageous in that they are painful to patients physically or psychologically. Accordingly, a reagent and a method for diagnosing Crohn's disease in vitro in a convenient and accurate manner are desired.
With regard to etiology of inflammatory bowel disease, it has long been reported that exogenous factors such as bacteria, viruses and alimentary antigens are related to intestinal inflammation. As for Crohn's disease in particular, there have been reported cases of infection and detection of Mycobacterium paratuberculosis (Non-patent documents 1 to 4, etc.); cases of detection of antibodies to baker's yeast and neutrophil (Non-patent documents 5 and 6, etc.), and cases of detection of an antibody to swine amylase or detection of an antibody to a Crohn's disease antibody binding peptide (see Patent documents 1 and 2). Some of these also reported antibodies specific to the disease, but none of them by itself showed a sufficient positive percentage for patients with Crohn's disease, posing a problem of a high false positive rate for ulcerative colitis which must be discerned therefrom. Under these circumstances, it is extremely important to develop a clinical test method by which Crohn's disease can be specifically diagnosed in a convenient and rapid manner at a high accuracy utilizing an antigen peptide specific to Crohn's disease.    Patent document 1: Japanese Patent Laid-Open (Kokai) No. H11-190734 (Claims)    Patent document 2: International publication WO 02/088175 (Disclosure of the Invention)    Non-patent document 1: Elsaghier A, et al. Clin Exp Immunol., 1992, 90, 503-508    Non-patent document 2: El-Zaatari F. A. et al. Curr Microbiol., 1999, 39, 115-119    Non-patent document 3: Naser S, et al. Vet Microbiol., 2000, 77, 497-504    Non-patent document 4: Suenaga K, et al. Dig Dis Sci., 1999, 44, 1202-1207    Non-patent document 5: Quinton J F, et al. Gut, 1998, 42, 788-791    Non-patent document 6: Peeters M, et al. Am J. Gastroenterol., 2001, 96, 730-734